The invention relates to a new reagent based on titanium(IV) compounds and a procedure for the determination of peroxides both in aqueous and in organic solutions.
Reagents and procedures for the qualitative or quantitative determination of peroxides in aqueous solutions are known. Odometric determinations using acid solutions of potassium iodide, determinations using the vanadium/sulphuric acid reagent known under the name of the Jorissen reagent, the titanium/sulphuric acid reagent and the titanium tetrachloride/hydrochloric acid reagent are customarily use. In general, these conventional reagents are suitable for the determination of hydrogen peroxide or inorganic peroxides which are soluble in an aqueous medium and which liberate hydrogen peroxide under the reaction conditions.
However, there is a great need for a reagent or procedure for the determination of peroxides in organic solutions. Particular importance is attached to peroxides which are produced in an uncontrolled manner by autoxidation in organic solvents. In this respect, exceptional danger and unpredictability are associated with hydroperoxides and polymeric peroxides which are formed in ethers, such as diethyl ether, diisopropyl ether, tetrahydrofuran and dioxane. On distillation of these solvents, these peroxides accumulate, even from an extremely low starting concentration, in the residue from distillation and can give rise to serious explosions. It is advisable, for reasons of safety, to have available a reagent for the accurate qualitative and quantitative determination of these peroxides. Moreover, it is also desirable to be able to determine other organic peroxide compounds, such as hydroperoxides and diperoxides, peracids, peresters and similar peroxy compounds.
However, the known reagents for the determination of peroxides in aqueous solutions are either unsuitable or only suitable in isolated exceptional cases for determinations in organic solutions. On the one hand, most of the conventional reagents have the disadvantage, that their reaction with peroxides is not specific and further that, in particular, polymeric peroxides are not detected. In addition, they frequently exhibit a sensitivity to atmospheric oxygen, and some of them to light as well, and this results in a considerable susceptibility to interference. On the other hand, the additional problem arises, in the determination of peroxides in organic solutions, that these reagents are not miscible with most organic solvents, and therefore two separate phases form. Moreover, decomposition reactions can occur with the solvents, sometimes with the formation of interfering colored decomposition products.
It is true that, in general, quantitative photometric methods are regarded as being very sensitive. However, because of the immiscibility, phase separation must precede photometric determinations of peroxides using the known reagents, and this makes procedures of this type elaborate and involves further sources of error. Because of the disadvantages which have been detailed, procedures of these types are assessed in the literature (see, for example, R. M. Johnson and J. W. Siddiqui: "The Determination of Organic Peroxides", Oxford, 1970) as being of low precision and unreliable. There is express advice against the use, for the determination of organic peroxides, of reagents based on titanium(IV) compounds which utilize the characteristic yellow-orange color of the peroxotitanyl cation, which is formed with hydrogen peroxide, and which are less sensitive to atmospheric oxygen (R. D. Mair and R. T. Hall: "Determination of Organic Peroxides by Physical, Chemical and Colorimetric Methods" in D. Swern: "Organic Peroxides", Vol. II, New York, 1971).
A need therefore continues to exist for a procedure for the determination of peroxides which is equally suitable for both aqueous and organic solutions, and for a generally applicable reagent suitable for use therein.